Steam holds an estimated 75% share of the PC game distribution market.
U.S. antitrust law and jurisprudence, courts generally look for a minimum threshold of more than 50%, with many federal courts requiring 70%
Steam has engaged in several anti competitive price fixing schemes already.
https://tech-insider.org/valve-10-publishers-steam-price-fixing-lawsuit-2026/
This is one of many cases. The devil is in the details, if you read the filings and previous testimony it becomes clear that Steam is fucking lying through its teeth and most definitely have engaged in monopoly practices.